feat(adb): use sticky event emitter for AdbServerClient.DeviceObserver.prototype.onListChange event

Author: yume-chan

libraries/adb-daemon-webusb/src/observer.ts

@@ -1,5 +1,5 @@
 import type { DeviceObserver } from "@yume-chan/adb";
-import { EventEmitter } from "@yume-chan/event";
+import { EventEmitter, StickyEventEmitter } from "@yume-chan/event";
 
 import {
     AdbDaemonWebUsbDevice,
@@ -34,7 +34,7 @@ export class AdbDaemonWebUsbDeviceObserver
     #onDeviceRemove = new EventEmitter<AdbDaemonWebUsbDevice[]>();
     onDeviceRemove = this.#onDeviceRemove.event;
 
-    #onListChange = new EventEmitter<AdbDaemonWebUsbDevice[]>();
+    #onListChange = new StickyEventEmitter<AdbDaemonWebUsbDevice[]>();
     onListChange = this.#onListChange.event;
 
     current: AdbDaemonWebUsbDevice[] = [];

libraries/adb/src/server/observer.ts

@@ -1,4 +1,4 @@
-import { EventEmitter } from "@yume-chan/event";
+import { EventEmitter, StickyEventEmitter } from "@yume-chan/event";
 
 import { Ref } from "../utils/index.js";
 
@@ -95,6 +95,17 @@ export class AdbServerDeviceObserverOwner {
             throw options.signal.reason;
         }
 
+        const onDeviceAdd = new EventEmitter<AdbServerClient.Device[]>();
+        const onDeviceRemove = new EventEmitter<AdbServerClient.Device[]>();
+        const onListChange = new StickyEventEmitter<AdbServerClient.Device[]>();
+        const onError = new StickyEventEmitter<Error>();
+
+        const observer = { onDeviceAdd, onDeviceRemove, onListChange, onError };
+        // Register `observer` before `#connect`.
+        // Because `#connect` might immediately receive some data
+        // and want to trigger observers
+        this.#observers.push(observer);
+
         this.#stream ??= this.#connect();
         const stream = await this.#stream;
 
@@ -103,14 +114,6 @@ export class AdbServerDeviceObserverOwner {
             throw options.signal.reason;
         }
 
-        const onDeviceAdd = new EventEmitter<AdbServerClient.Device[]>();
-        const onDeviceRemove = new EventEmitter<AdbServerClient.Device[]>();
-        const onListChange = new EventEmitter<AdbServerClient.Device[]>();
-        const onError = new EventEmitter<Error>();
-
-        const observer = { onDeviceAdd, onDeviceRemove, onListChange, onError };
-        this.#observers.push(observer);
-
         const ref = new Ref(options);
 
         const stop = async () => {

libraries/event/src/event-emitter.ts

@@ -62,7 +62,7 @@ export class EventEmitter<TEvent, TResult = unknown> implements Disposable {
 
     fire(e: TEvent) {
         for (const info of this.listeners.slice()) {
-            info.listener.apply(info.thisArg, [e, ...info.args]);
+            info.listener.call(info.thisArg, e, ...info.args);
         }
     }
 

libraries/event/src/index.ts

@@ -1,4 +1,5 @@
 export * from "./disposable.js";
-export * from "./event.js";
 export * from "./event-emitter.js";
+export * from "./event.js";
+export * from "./sticky-event-emitter.js";
 export * from "./utils.js";

libraries/event/src/sticky-event-emitter.ts

@@ -0,0 +1,23 @@
+import { EventEmitter, type EventListenerInfo } from "./event-emitter.js";
+import type { RemoveEventListener } from "./event.js";
+
+export class StickyEventEmitter<TEvent, TResult = unknown> extends EventEmitter<
+    TEvent,
+    TResult
+> {
+    #value: TEvent | undefined;
+
+    protected override addEventListener(
+        info: EventListenerInfo<TEvent, TResult>,
+    ): RemoveEventListener {
+        if (this.#value) {
+            info.listener.call(info.thisArg, this.#value, ...info.args);
+        }
+        return super.addEventListener(info);
+    }
+
+    override fire(e: TEvent): void {
+        this.#value = e;
+        super.fire(e);
+    }
+}